The transient kinetics of reaction of enzyme with substrate and/or substrate analogs are being investigated by electronic vibronic spectroscopic changes relating to changes in the structure of both substrate and protein. The enzymes which have been most avidly investigated are glyceraldehyde-3-PO4-dehydrogenase (GPDH), alcohol dehydrogenase, phosphoglycerate kinase (PGK), acetylcholinesterase and Na ion -K ion ATPase. In addition to enzyme-substrate interactions, the kinetics and equilibria of enzyme-ligand interaction has been studied for a variety of physiologically and/or functionally significant factors of the above enzyme activities. In all cases studied, the role of the effector is to stabilize a particular protein conformation which is either necessary for (positive effectors) or incapable of (negative effectors) enzymic catalysis. In the case of GPDH, we have observed the activation of acyl-enzyme for catalytic reduction, and for phosphorolysis directly via spectroscopic-kinetic techniques. The quaternary structure of GPDH is perturbed by reaction (acylation) and by interaction with nucleotides and dinucleotides. Under particular conditions of effector concentrations, enzyme concentration and solvent the enzyme associates with PGK.